1. Field of the Invention
This invention relates to an electric circuit and sensor for detecting arcing and a transparency having the sensor, and more particularly, to an electric circuit and sensor for detecting arcing of an electrical heating system of an aircraft transparency, e.g. a laminated aircraft windshield and to a laminated aircraft windshield having portions of the electric circuit and sensor.
2. Discussion of the Available Technology
Aircraft or aerospace windows, e.g. aircraft windshields include a laminate of plastic layers or sheets, glass layers or sheets and combinations thereof. The layers of an inner segment of the windshield face the interior of the aircraft and provide structural stability to the windshield. The layers of an outer segment of the windshield face the exterior of the aircraft. The outer segment of the windshield, which can also provide structural stability, is usually provided with accessories for visual acuity. For example and not limiting to the discussion, the outer segment of the windshield can include an electrical conductive coating, or a plurality of electrical conductive wires, between and connected to a pair of spaced bus bars to heat the outer surface of the windshield to prevent the formation of fog, snow and ice, and/or to remove fog, snow and ice from, the surface of the windshield facing the exterior of the aircraft, also referred to as the outer surface of the windshield.
As is appreciated by those skilled in the art, as the service or operating time of the aircraft windshield increases, the operating efficiency of the windshield decreases until such time that the accessories of the windshield become non-functional, and the windshield needs to be replaced or repaired. More particularly and not limiting to the discussion, the peripheral edge of the windshield has an outboard moisture seal that is a barrier to prevent moisture from entering between the plastic and glass layers or sheets of the windshield. When the seal fails, e.g. cracks and/or the layers de-bond due to erosion caused by wind and rain; moisture enters between the layers of the windshield. While the cracking or de-bonding of the seal is not a structural issue, when moisture moves between the layers of the windshield, the windshield can de-laminate, and the conductive coating or wires, whichever is present, can be damaged and fail, thereby reducing the service life of the windshield. More particularly, when delamination of the windshield occurs, increased amounts of moisture move between the layers of the windshield accelerating the degradation of the windshield, e.g. causing arcing, damage and/or failure of the bus bars and the electrical conductive coating or wires thereby reducing or eliminating the defrosting capabilities of the windshield.
At the present time sensors for detecting arcing are available, e.g. disclosed in the above-mentioned U.S. patent application Ser. Nos. 12/345,932 and 12/345,952. Although the presently available sensors for detecting arcing are acceptable, they have limitations. For example, but not limiting to the discussion, the presently available sensors for detecting arcing of an electrical conductive coating between two bus bars measures the current at a first bus bar and the current at a predetermined position on the conductive coating or at the second bus bar. When the difference between the two measurements exceeds a predetermined current difference, a signal is forwarded to a control system to discontinue the current input to the bus bars. This type of sensor does not take into account that the current to the bus bars includes electric noise and interference that results from the airplane generator providing electrical power to the aircraft transparency, the lights, the air conditioner and other electrical equipment of the aircraft. As a result, the readings are not an accurate representation of current variations caused by arcing.
Based on the preceding discussion, it can be appreciated by those skilled in the art that it would be advantageous to provide an electric circuit and sensor for detecting arcing, and a transparency having components of the circuit and sensor, that eliminates the limitations of the presently available electric circuits and sensors for detecting arcing.